The Program Project application is concerned with basic phenomena of conception and early pregnancy in mammals. The general objectives are: 1) To study in depth the stages of conception and early pregnancy in mammals whose failure has been identified as possibly leading to infertility, or whose vulnerability may lead to new methods of controlling fertility. Since it is virtually impossible to study in detail these phases of human reproduction, we propose to study mechanisms which are specific to the reproductive processes of mammals, and pursue their regulation in depth. 2) The topics to be investigated include spernatogenesis, oogenesis, fertilization, cleavage and implantation. Emphasis is placed on the kinetic aspects of early development in the mammal and the interactions of the preimplantation stages with the local environment where the preimplantation embryonic stages develop within the female genital tract.